Direct transrectal infiltration of the prostate with antibiotics was performed in 25 selected patients with refractory chronic prostatitis, and sequential samples of urine and prostatic secretion were studied at 3-monthly intervals thereafter. The criterion for cure of chronic bacterial prostatitis was persistently sterile cultures of urine and prostatic secretion for at least 12 months after completion of treatment. Complete cure was obtained in 14 patients (56%) after one or two infiltrations. In seven other patients clinical and bacteriologic remission was obtained after several injections but the follow-up period was too short to judge the efficacy of the intraprostatic antibiotic administration. The remaining four patients (16%) had sterile specimen cultures 3 months after one injection, but were lost to further follow-up. The results suggest that local antibiotic treatment of chronic bacterial prostatitis is useful, although careful randomized studies with long follow-up are required to evaluate the merits of the method.